The invention relates to the layerwise SZ stranding of elements to be stranded, for instance, to the stranding of elements of electric cables, such as wires, conductors, conductor pairs or star quads, or also to the stranding of optical transmission elements for optical cables such as are being used more recently in the field of communication cable technology.
Various methods and apparatus for the layerwise SZ twisting of elements to be twisted have been developed since the beginnings of SZ twisting. In general, a cabling disc revolving with alternating direction of rotation has essentially been provided as the twisting member proper for this purpose.
A particular difficulty in the development of suitable methods and machine designs for layerwise SZ twisting is the requirement that the twisting should lead to distances as large as possible between the reversal points of the twist direction in the stranded material produced. It has been possible to increase the original distances of about one twist length (U.S. Pat. No. 2,924,930) to two or three times that amount by using additional cabling discs. The additional cabling discs then form, ahead of the main cabling apparatus, a device for suppressing undesired entanglements (U.S. Pat. Nos. 3,187,495 and 3,133,402) as well as also a kind of storage for the twisting lays executed by the cabling disc in the backward direction. In the simplest case, a single additional cabling disc is provided, which is arranged fixed at a considerable distance ahead of the oscillating cabling disc and serves merely for the defined feeding of the elements to be twisted to the oscillating cabling disc (German Offenlegungsschrift 24 11 151, FIG. 1, and German Offenlegungsschrift 24 55 062, FIGS. 1 and 2). A tube, onto which the twist lays are placed, can be arranged between the stationary and the oscillating cabling disc. However, the storage capacity of such a tube is small because of the friction losses.
The storage capacity of the storage device arranged ahead of the twisting means and thereby, the distance of the reversal points of the twist direction in the twisted material can be increased by associating a relatively long, flexible tubular guide with each element to be twisted. The guide is arranged such that one end is rotatable with the twisting means and the other end is stationary (U.S. Pat. No. 3,847,190). The application of such a storage device to the layerwise stranding of elements to be stranded leads to difficulties, however, because the axially fixed flexible tubular guides are then stranded on the core strand which is being transported axially.
For the normal SZ twisting of elements to be twisted, in which the elements to be twisted are twisted together not in layers but directly (in bundles), apparatus is furthermore known which likewise contains an oscillating cabling disc as the twisting means proper and in which the twist angle is increased substantially by the provision that a twisting closer into which the elements to be twisted run, is disposed at a fairly large distance ahead of the cabling disc. This does not suppress the twisting action exerted by the cabling disc in the backward direction but brings it on intentionally, and distributes it over a longer section of the material to be twisted (U.S. Pat. No. 4,056,925).